1. Field of the Invention
This invention relates to ice condenser containments, also known as ice baskets, employed for condensing steam generated from the primary water of a nuclear reactor in the event of an accidential loss of coolant and, more particularly, to a removable cruciform which may be employed as a replacement for the original, nonreplaceable cruciforms of conventional ice baskets, or as an original assembly component of an improved ice basket.
2. State of the Relevant Art
Ice condenser containments, also known as ice baskets, are employed with nuclear reactors for condensing the steam from the primary water of the reactor in the event of an accidental loss of coolant. In a typical installation, there are provided approximately 2,000 ice baskets, each of which is approximately one foot in diameter and 48 feet in height and is filled with approximately 1,500 pounds of ice. The sidewalls of the ice basket, substantially cylindrical in configuration, are perforated to permit rapid exposure of the steam to the ice and corresponding, rapid cooling.
Each such ice basket incorporates, at spaced intervals therein, stiffening rings comprising structural elements which provide lateral rigidity and support, to accommodate not only the weight of ice contained therein but also seismic and other disturbances. Conventional ice baskets furthermore include elements known as cruciforms, comprising generally x-shaped metal straps which extend diametrically across the interior of the basket and are welded at the ends of the straps to the interior sidewalls of the basket, typically at or adjacent the stiffening rings. Typically, the cruciforms are formed of 1/8 inch thick metal, and are 11/2 inches in height. Further, typically, seven (7) such cruciforms are assembled within the basket, spaced at approximately six (6) foot vertical intervals. While not structural members of the baskets and thus not necessary to add radial stiffness to the ice basket cross-section, the cruciforms are necessary elements for satisfying various requirements of the ice bed within the basket. For example, cruciforms are necessary to assure that the geometry of the ice bed within the basket is contained during the entire meltout period of a postulated loss of coolant accident. Specifically, as the ice melts upwardly and away from the bottom of the ice baskets, ice contained therein at higher elevations cannot be permitted to fall down into the bottoms of the baskets, since this presents the potential of creating bypass flow routes for the emerging steam which would accompany the loss of coolant. The cruciforms also serve to prevent large masses of ice from falling during seismic disturbances; falling masses of ice could impose unacceptable impact loads on the ice basket and related, underlying supporting structure.
The presence of the cruciforms, however, compounds a maintenance problem which exists in the operation of nuclear power systems employing such ice condenser containments. Particularly, due to sublimation of the ice, the initial volume and weight thereof decreases with time and thus the ice must be replenished, or replaced. A minimum required amount of ice is typically at least 1,200 pounds for each ice basket, for assuring its effectiveness for counteracting the accidental loss of coolant, as above referenced. The cruciforms impose a substantial obstacle to replenishing the supply of ice, as the latter is depleted due to sublimation. For example, the successively lower compartments of the basket, as delineated by the cruciforms, may contain inadequate charges of ice due to sublimation loss, which changes remain spaced apart due to the presence of cruciforms. Thus, while access may be had to the upper, open end of the ice basket for recharging the first and possibly the second upper compartments, the lower compartments are inaccessible, yet may contain an inadequate charge of ice. The ice basket thus loses its required cooling capability, presenting a potentially serious deficiency in its required coolant capacity.
Various solutions have been proposed heretofore to overcome the problems thus presented in the replenishment of the ice in view of the obstacles presented by the cruciforms. One such solution is the removal of the original cruciforms, as permitted in view of their not comprising a structural support element of the basket. A known, replaceable cruciform design exists which has been proposed for installation in place of the previously permanent, but removed, original cruciforms. The replaceable cruciform of known design requires that it be rotated onto its side, effectively reducing its width such that it can be passed downwardly through the ice basket; at the desired elevation for installation, the cruciform then must be rotated back to a horizontal position. Individual, spring-activated locking devices then are released by remote actuation from the top open end of the ice basket, by tools which afford the requisite reaching length into the ice basket, so as to lock the cruciform onto the coupling or stiffening ring within the basket at the corresponding elevation. The known, replaceable cruciform, however, is extremely difficult to install and remove, and is virtually impossible to install at elevations within the ice basket lower than approximately 42 feet from the open top thereof.
Accordingly, there exists a need for a removable cruciform which is readily installed or removed, at every required elevation within the ice basket.